The present invention relates to a copying apparatus and an optical assembly usable therewith, wherein an optical member is used for imaging an original to be copied on a photosensitive member, which optical member comprises a plurality of small imaging elements arranged in the direction crossing the optical axes of the elements.
Generally, an array or arrays of a number of small-diameter bar-like imaging elements or bar lenses arranged in a direction transverse with thee optical axes thereof (hereinafter called a small-diameter imaging element array or imaging element array) is designed to form an image of an original at a unit magnification, the small-diameter bar-like imaging elements being known, for example, as "SELFOC" (trandemark, available from Nippon Ita Garasu Kabushiki Kaisha, Japan) which is used in a copying apparatus as imaging means and has a parabolic refractive index distribution decreasing radially outwardly and is effective to transmit the incident light in a wave-like fashion. FIG. 1A illustrates an example of a unit magnification imaging element array 4 used with a copying apparatus. The imaging element array 4 consists of a number of imaging elements 4a which are arranged parallel as a unit, and each of which is effective to form an image at a unit magnification. The imaging element array 4 is disposed equidistant from the information surface 1a of the original 1 and the photosensitive surface 3a of the photosensitive drum 3 so as to form an image of the original surface 1a onto the photosensitive surface 3a at a unit magnification.
Japanese Laid-Open Patent Application No. 16415/1982, corresponding to U.S. Pat. No. 4331380, discloses an imaging element array for forming a reduced or enlarged image. FIG. 1B illustrates an imaging element array 2 for reduction, disclosed in the Japanese Patent Application. The imaging element array 2 consists of a number of imaging elements 2a, each of which is effective to form a reduced image. The central imaging element in the imaging element array is positioned substantially perpendicular to the original surface 1a and to the photosensitive surface 3a. The other imaging elements are arranged in a fan-like fashion so that the elements are inclined more as the distance from the central imaging elements increases. In the arrangement of this Figure, the imaging element array 4 is offset toward the photosensitive surface 3a in consideration of the imaging distance, so that a reduced image of the original surface 1a is formed on the photosensitive surface 3a. If the imaging element array 2 is positioned upsidedown, and if it is offset toward the original surface 1a, an enlarged image of the original can be formed on the photosensitive surface 3a. The imaging element arrays are also disclosed in U.S. Pat. No. 4,405,207. Additionally, an example of a reduction imaging element array is disclosed in U.S. Pat. No. 4,168,900, which uses bar lenses as the imaging elements.
It has been proposed, in U.S. Pat. Nos. 4,331,380, 4,394,083, for example, to equip an image forming apparatus with a plurality of imaging element arrays which are for unit magnification, reduction or enlargement image formation as described above, so as to make it perform a variable magnification projection. FIG. 2 shows an example thereof, wherein a reduction imaging element array 2 and a unit magnification imaging element array 4 are juxtaposed integrally movable below the original document surface 1a. Below those element arrays, a photosensitive drum 3 is dispoesd. At a suitable position adjacent to the imaging element arrays 2 and 4, there is provided a fluorescent lamp 5 and an auxiliary reflection mirror 6 for reflecting the illumination light emitted by the fluorescent lamp 5. The imaging magnification can be switched between the unit magnification and the reduction by translating integrally the imaging element arrays 2 and 4 in the direction shown by an arrow 7.
The following problems arise in this apparatus. Firstly, it necessarily requires a driving mechanism for switching the positions of the imaging element arrays and a space for accommodating the imaging element array not being used. This is in contradiction to the fundamental purpose of the use of imaging element arrays, that is, to reduce the size of the exposure device. Secondly, the number of the magnification variation is determined by the number of the built-in imaging element arrays, so that the number can not be increased unless a large space is given for the non-used imaging element arrays. Thirdly, the switching mechanism mentioned above is complicated so as to increase the cost of the apparatus.
The prior art also teaches another structure in which the two imaging element arrays are fixed, and a shutter is moved under the arrays to switch the imaging element arrays to be used. However, this also requires a complicated mechanism to move the shutter. In addition, since the imaging element arrays are fixed, the apparatus is required to be bulky if the number of usable magnifications is increased. Furthermore, since those positions on the original surface or on the photosensitive surface which are faced by the two imaging element arrays, are different, the illumination of the original has to be made at a high intensity and over a broad area, or it makes difficult the use of a small diameter drum as the photosensitive member, or it makes difficult the increased number of usable magnifications.